Silicon on Sapphire (SOS) wafers are a type of substrate material commonly used in the microelectronics and semiconductor industries. The wafer consists of a single crystal sapphire substrate with a thin layer of silicon deposited on top. The sapphire substrate provides a high-strength base and the silicon layer provides a surface for the active devices to be built upon. The combination of the two materials offers advantages such as high thermal stability, high mechanical strength, and high electrical insulation, making it an ideal material for high-temperature and high-power electronic devices. Some common applications for SOS wafers include high-frequency power amplifiers, high-temperature sensors, and high-power microwave devices.